This invention generally relates to breast prostheses and methods for manufacturing breast prostheses. More specifically, this invention relates to breast prostheses having a biocompatible outer shell which is stronger than more conventional designs. The present invention encompasses implants and the like wherein the outer shell includes a non-woven spun surface bonded to a non-porous outer envelope. The porous surface of the spun polyurethane promotes tissue ingrowth and may be further treated with a silicone rubber material to render it more crack resistant under in vivo conditions.
The typical breast prosthesis includes a silicone outer shell filled with a silicone based gel. The development and use of such implants generally began with the surgical injection of silicone gel under the skin to fill out wrinkles and to enlarge the breast. Due to the extensive migration of the silicone gel after injection, a sack or shell, typically made of silicone rubber, was adopted for use in such implants to enclose the gel and to prevent migration after implantation. Such a design which includes a silicone rubber outer shell is typical of modern breast implants. Such implants present several problems due to the nature of their construction and the materials selected therefor.
The silicone gel which is often used as a filler material within the silicone outer shell of the conventional prosthesis typically contains unreacted silicone oils. Such oils have been known to permeate through the silicone shell of the prosthesis and to find their way into the lymph nodes of the body, thereby presenting a potential cancer risk to the patient. Furthermore, the outer silicone rubber shell is inherently weak and cases have been documented wherein these outer shells have ruptured following implantation in the body. Consequently, an outer shell having a tensile strength higher than that of silicone rubber would be desirable.
The smooth wall of the typical silicone rubber outer shells of conventional breast implants are also believed responsible, at least in part, for contracture and migration of the prosthesis after implantation in a patient. Such a condition, commonly referred to as capsular contracture, results from the build up of hard scar tissue around the implant which can eventually cause contraction and some migration of the implant. This condition can become quite painful for the patient and can require additional surgery to break the capsule and perhaps remove the implant.
The present invention overcomes the aforementioned problems by providing a breast implant which is manufactured with an outer shell made of a material which is impermeable to the oils contained in the silicone gel filler material which is often used in such prostheses. The outer shell of the implant of the present invention is significantly stronger than prior art silicone rubber outer shells and is provided with a porous surface made of a non-woven polymer fiber which promotes tissue ingrowth.
In a preferred embodiment, the implant of the present invention is manufactured with an outer shell which includes a non-porous outer envelope and a porous outer layer on the outer surface of the envelope. The porous outer layer is made by spinning polymer fibers onto the smooth surface of the shell to build up a porous three dimensional structure which, after implantation, will promote tissue ingrowth. Most preferably, the outermost porous layer is manufactured with a polycarbonate urethane polymer which is highly resistant to in vivo cracking. The non-porous envelope may also be manufactured from a polycarbonate urethane polymer. When the aforementioned porous layer is manufactured from polyurethane materials other than polycarbonate urethane polymers, or from other polymers generally, in vivo cracking may be a problem which can be avoided by treating the fibers of the porous layer with a silicone-rubber material to render the fibers more crack resistant. A similar treatment of the non-porous outer envelope can be accomplished. The pores within the outer layer can be filled with an appropriate gel containing elutable drugs such as antimicrobials or antibiotics which may be bound to protamine to reduce the incidence of infection following implantation. Other useful drugs may be used such as steroids, heparin, corticoids, chemotherapy drugs, and the like.
In a preferred method for manufacturing the implant of the present invention, the shell is made on a polished and shaped mandril by dip-coating or pour-coating with an appropriate elastomer such as polyurethane or silicone rubber in a solvent, for example. The elastomer is cured or dried to form the non-porous outer envelope of the outer shell. Alternatively, the non-porous outer envelope of the outer shell can be made by rotational casting of the reactants of a polyurethane or a silicone rubber or by melting fine powders of a polyurethane.
While still on the mandril the envelope is placed on an electrically grounded rotating cup and rotated. A spinnerette is positioned over the rotating shell and is charged to a desired voltage. Fibers are extruded from the spinnerette and attracted to the grounded prosthesis under controlled temperature and humidity conditions to thereby provide a porous three dimensional outer layer which is bonded to and surrounds the non-porous outer envelope. Alternatively, the porous three dimensional outer layer can be made separately by electrostatically spinning polyurethane fibers onto a polished metal mandril and then removing the resulting structure from the mandril and placing it over the non-porous shell. The porous layer can be affixed to the outer shell of the implant either by use of an appropriate adhesive or by treating the outer shell with an appropriate solvent to promote bonding between the fibers and the smooth outer envelope. The porous outer layer and non-porous shell may be further treated with a silicone-rubber material to render the fibers more resistant to biodegradation under in vivo conditions.
The material used to fill the implant of the present invention may include the aforementioned silicone gels as well as other suitable substances known by those skilled in the art.
Accordingly, it is an object of the present invention to provide an implantable breast prosthesis which includes an outer shell which includes a non-porous outer envelope and a porous outer layer.
It is another object of the present invention to provide the aforementioned breast prosthesis with a porous three dimensional outer layer to promote tissue ingrowth after implantation in a patient.
It is still another object of the present invention to provide a method for the manufacture of a breast prostheses which includes electrostatically spinning a polymer material to form a three dimensional porous structure which will promote tissue ingrowth after implantation in a patient.
These and other objects of the present invention will be further appreciated by those skilled in the art following a review of the remainder of the present disclosure including the detailed description of the preferred embodiment and the claims.